1. Field of the Invention
The present invention relates to a noncontact laser-based surface measuring apparatus.
2. Description of the Related Art
It is known that a laser-probe-based form measuring apparatus having a laser autofocusing function can widely measure the form and roughness of a precision part at a resolution of nanometers. For example, a noncontact form measuring apparatus disclosed in U.S. Pat. No. 7,209,242/EP1555561 measures an objective work on three-dimensional orthogonal coordinate axes X, Y, and Z by directing a laser beam onto a top face of the work, autofocusing the laser beam in a vertical (Z-axis) direction, scanning the work in the X- and Y-axis directions, detecting Z-axis movements of an objective optical system in an autofocusing optical system, and collecting data related to a surface form of the work based on the detected Z-axis movements.
According to the related art, the laser beam serves as a probe beam that is substantially a ray of light. The laser beam advances in parallel with an optical axis of the objective optical system, enters the objective optical system at a point out of the optical axis, and crosses the optical axis on a focal plane of the objective optical system. The position where the laser beam crosses the optical axis is positionally fixed to the objective optical system, and therefore, moving the objective optical system relative to the work in the Z-axis direction results in moving the position of the laser beam on the surface of the work in the X- or Y-axis direction. The laser beam reflected by the surface of the work is transmitted through the objective optical system and is detected by a position detector to detect a position of the reflected beam. From the detected position of the reflected beam, a positional deviation is measured between the surface of the work and the focal plane of the objective optical system. The measured positional deviation is feedback for autofocusing. From Z-axis positions of the objective optical system obtained through these steps, a surface form of the work is measured.